Meteorite ordinary chondrite

Figure 7 shows the abundances of the four refractory lithophile elements—aluminum, calcium, scandium, and vanadium—in several groups of undilferentiated meteorites, the Earth s upper mantle and the Sun. The RLE abundances are divided by magnesium and this ratio is then normalized to the same ratio in Cl-chondrites. These (RLE/Mg)N ratios are plotted in Figure 7 (see also Figure 1). The level of refractory element abundances in bulk chondritic meteorites varies by less than a factor of 2. Carbonaceous chondrites have either Cl-chondritic or higher Al/Mg ratios (and other RLE/Mg ratios), while rumurutiites (highly oxidized chondritic meteorites), ordinary chondrites, acapulcoites, and enstatite chondrites are depleted in refractory elements. The (RLE/Mg)N ratio in the mantle of the Earth is within the range of carbonaceous chondrites.

Figure 18 versus for chondritic meteorites. Ordinary chondrites (H, L, LL, and R) plot above the... 

In Nature, an additional mineral, nierite (Si3N4), was found in the perchloric acid-resistant residues of primitive meteorites (ordinary chondrites [29] and enstatite chondrites [30, 31]) [32]. This mineral was seen to occur in lathe-shaped grains that were 2 pm x 0.4 pm in size. An inspection of the mineral by using selected area electron diffraction (SAED) showed the d-spacings of nierite to be comparable to those of synthetic a-Si3N4. The unit-cell parameters of nierite, as calculated from measured d-spadngs, were a = 0.774 0.002 nm, c = 0.561 0.002 nm, while the calculated density was 3.11 gcm [33]. 

Other meteorite classes like C2, CO and ordinary chondrites contain much smaller inclusions less than 1 mm (MacPherson et al. 1988) and require ion microprobe techniques to evaluate the isotopic compositions. On the least metamorphosed side. Cl have very few inclusions or oxide grains, but are the carrier of the greatest amounts of stellar nanodiamond and other carbides (Anders and Zirmer 1993). As will be shown for Cr anomalies in carbonaceous chondrites, the survival of the mineral carriers of the anomalies also depends on the metamorphic grade of the meteorites. Nevertheless, isotopic anomalies have also been formd in higher metamorphic grade from other classes, especially in the reduced enstatite chondrites. 

Figure 8. Figure (a) after Clayton et al. (1976, 1977). The scales are as in Figure 1. The O isotopic compositions of the different meteorite classes are represented ordinary chondrites (H, L, LL), enstatite chondrites (EFl, EL), differentiated meteorites (eucrites, lAB irons, SNCs) and some components of the carbonaceous chondrites. As the different areas do not overlap, a classification of the meteorites can be drawn based on O isotopes. Cr (b) and Mo (c) isotope compositions obtained by stepwise dissolution of the Cl carbonaceous chondrite Orgueil (Rotaru et al. 1992 Dauphas et al. 2002), are plotted as deviations relative to the terrestrial composition in 8 units. Isotopes are labeled according to their primary nucleosynthetic sources. ExpSi is for explosive Si burning and n-eq is for neutron-rich nuclear statistical equilibrium. The open squares represent a HNOj 4 N leachate at room temperature. The filled square correspond to the dissolution of the main silicate phase in a HCl-EIF mix. The M pattern for Mo in the silicates is similar to the s-process component found in micron-size SiC presolar grains as shown in Figure 7.

Busfield A, Gilmour JD, Whitby JA, Turner G (2004) Iodine-xenon analysis of ordinary chondrite halide implications for early solar system water. Geochim Cosmochim Acta 68 195-202 Busso M, Gallino R, Wasserburg GJ (1999) Nucleosynthesis in asymptotic giant branch stars relevance for galactic enrichment and solar system formation. Annu Rev Astronom Astrophys 37 239-309 Cameron AGW (1969) Physical conditions in the primitive solar nebula. In Meteorite Research. Millman PM (ed) Reidel, Dordrecht, p 7-12... 

Choi BG, Huss GR, Wasserburg GJ, Gallino R (1998) Presolar corundum and spinel in ordinary chondrites origins from AGB stars and a supernova. Science 282 1284-1289 Christophe M (1968) Un chondre exceptionnel dans la meteorite de Vigarano. Bui Soc Er Mineral Cristallogr 91 212-214... 

Huss GR, MacPherson GJ, Wasserburg GJ, Russell SS, Srinivasan G (2001) Aluminum-26 in calcium-aluminum-rich inclusions and chondrales from unequilibrated ordinary chondrites. Meteorit Planet Sci... 

Chondrules from Chainpur LL3 meteorite have somewhat lower 5 Mg values than Chainpur LL3 matrix. Cl, and terrestrial mantle clinopyroxene. Chondrules from the Bjurbole L/LL4 ordinary chondrite also have slightly lower 8 Mg values than Cl and LL3 matrix. Chondrules, matrix, and whole rock samples from the Allende CV3 meteorite span a larger range in 5 Mg that overlaps the Cl and ordinary chondrite data. 

Variability in Mg isotope ratios among chondritic meteorites and their constituents is dominated by mixing between a radiogenic CAI-like reservoir and a reservoir resembling ordinary chondrites. The mixing is evident in 5 Mg and 8 Mg, Al/Mg, and A 0 values but... 

The Ca isotope ratios of meteoritic samples are of interest because they can give information on early solar system processes and because meteorites represent the materials from which the Earth accreted and hence relate to the expected values for the bulk Earth. Russell et al. (1978b) made the first measurements of stable Ca isotope variations in meteorites. They formd variations of about +l%o for the Ca/ Ca ratio in samples from six different meteorites. Although some of these samples were spiked after having separated the Ca with an ion exchange column and hence may contain artifacts, it is clear from their data that bulk meteorites have some variability in 8 Ca and that the average value is quite close to the terrestrial standard. No data on bulk meteorites have been reported since the Russell et al. (1978b) measurements, and since their one measurement of an ordinary chondrite had a poor Ca column yield, there exist no reliable measurements that can be used to verify the composition of typical chondritic meteorites. 

Robert F, Epstein S (1982) The concentration and isotopic composition of hydrogen, carbon and nitrogen carbonaceous meteorites. Geochim Cosmochim Acta 46 81-95 Robert F, Merlivat L, Javoy M (1978) Water and deuterium content in ordinary chondrites. Mete-oritics 12 349-354... 

The characteristics of the presolar diamonds also change with the metamorphic grade of the host meteorite. F igure 5.15 shows the typical bimodal release of heavy noble gases (here illustrated by xenon) in Orgueil, an unheated chondrite. This pattern is compared to the xenon-release patterns of two ordinary chondrites that have experienced different degrees of mild metamorphism. The amount of low-temperature gas, labeled P3 for historical reasons, is a sensitive function of temperature. Its abundance correlates well with other indicators of... 

Wlotzka, F. (1993) A weathering scale for the ordinary chondrites. Meteoritics, 28, 460. 

Ion probe (SIMS) measurements of (26Al/27Al)0 for chondrules from several meteorite groups. The right axis shows the formation time relative to CAIs, the oldest solids formed in the solar system. These data indicate that chondrule formation started at least 1 Myr after CAIs formed and continued for 1-2 Myr. For CR chondrites, in addition to the plotted data, a similar number of chondrules show no resolvable evidence for 26Al. Data for unequilibrated ordinary chondrites (UDC) from Kita ef al. 

Huss, G. R., Tachibana, S. and Nagashima, K. (2007) 26A1 and 60Fe in chondrules from unequilibrated ordinary chondrites. Meteoritics and Planetary Science, 42, A57. 

Schmitz, B., Tassinari, M. and Peucker-Ehrenbrink, B. (2001) A rain of ordinary chondritic meteorites in the early Ordovician. Earth and Planetary Science Letters, 194, 1-15. 

As already noted, spectral similarities between the various asteroid classes and specific types of meteorites provide a way to identify possible meteorite parent bodies. The Tholen and Barucci (1989) asteroid taxonomy has been interpreted as representing the types of meteorites shown in Table 11.1. Using the Bus et al. (2002) taxonomy, the C-complex asteroids are probably hydrated carbonaceous chondrites (e.g. Cl or CM). These carbonaceous chondrite asteroids probably accreted with ices and will be considered in Chapter 12. Some S-complex asteroids are ordinary chondrite parent bodies, but this superclass is very diverse and includes many other meteorite types as well. The X-complex includes objects with spectra that resemble enstatite chondrites and aubrites, and some irons and stony irons, although other X-complex asteroids are unlike known meteorite types. A few asteroid spectra are unique and provide more definitive connections, such as between 4 Vesta and... 

Anhydrous planetesimals, and especially the meteorites derived from them, provide crucial cosmochemical data. Spectroscopic studies of asteroids do not provide chemical analyses, but the spectral similarities of several asteroid classes to known meteorite types provide indirect evidence of their compositions. The few chemical analyses of asteroids by spacecraft are consistent with ordinary chondrite or primitive achondrite compositions. Laboratory analyses of anhydrous meteorites - chondrites, achondrites, irons, and stony irons - allow us to study important chemical fractionations in early solar system bodies. Fractionations among chondrites occur mostly in elements with higher volatility, reflecting the accretion of various components whose compositions were determined by high- and low-temperature processes such as condensation and evaporation. Fractionations among achondrites and irons are more complex and involve partitioning of elements between melts and crystals during differentiation. 

Slater-Reynolds, V. and McSween, H. Y. (2005) Peak metamorphic temperatures in type 6 ordinary chondrites an evaluation of pyroxene and plagioclase geothermometry. Meteoritics and Planetary Science, 40, 745—754. 

The least metamorphosed ordinary chondrites (petrologic types 3.0-3.1) show evidence of minor aqueous alteration that primarily affected the matrix, but in some cases also affected chondrule mesostasis. In these meteorites, the amount of aqueous fluid was very small, limiting the degree of alteration. 

The diamonds first recognized by Lewis et al. (1987) have now been traced to every class of chrondritic meteorite (Alexander et al. 1990 Huss 1990 Russell et al. 1991) and are known to occur as a component within the matrix. The amounts available for extraction reach a maximum of 900 ppm but decline to nothing in higher petrologic grades. The cut-off point in unequilibrated ordinary chondrites is about type 3.6 but for enstatite chondrites the type 4s still contain diamond. Progressive... 

In all but one type of chondrite, small millimeter-sized spherical silicate grains are trapped in the mineral matrix. These small grains consist mainly of amorphous silicates and are called chondrules. This latter term gives its name to the meteorite class containing chondrules, i.e. the chondrite class. The chondrites themselves are divided into three subclasses enstatite, ordinary chondrites and carbonaceous chondrites. Carbonaceous chondrites themselves are classified into four groups I (for Ivuna), M (for Mighei), O (for Omans) and V (for Vigarano). 

---